A bearing assembly for use in extreme conditions often encounters dirt and mud which in time can accumulate and pack against sealing structure and push contaminants into the bearing cavity. Maintenance-free bearings cannot be easily lubricated, and therefore the foreign material typically cannot be flushed away. In applications where power washers are used to clean areas around the bearing, contaminants are often forced into the bearing cavity by the cleaning process. Once a bearing is contaminated, the bearing will eventually seize and fail to turn or become loose due to wear.
Contamination problems are particularly apparent in agricultural tillage implement bearings such as disk bearings operating in wet and muddy soil conditions. Mud packing and pushing against the seals compromises the contaminant protection of the bearing seals. Extreme temperature conditions and freezing of material around the bearing increases exposure to contamination. Several times a year such bearings may be exposed to high pressure washing, further increasing the contamination problem. Although bearing assemblies such as shown in U.S. Pat. No. 4,249,782 assigned to Deere & Company, have generally performed well most of the time, incidences of failure caused by the harsh environmental operating conditions still occur.